Atrial systoleIsovol. contractionRapid ejectionReduced ejectionIsovol. relaxationRapid ventricular filling 0 0.1 0.2 0.3 0.4 0.60.5 0.7 0.8 Time (sec) Ventricular systole S P P R c a 4 1 2 3 v T Q Left atrial pressure Mitral valve opens Mitral valve closes Left ventricular pressure Aortic valve opens Aortic valve closes Aortic pressure Heartsounds VenouspulseElectrocardiogram •Fig. 16.39 Leftatrial,aortic,andleftventricularpressurepulsescorrelatedintimewithaorticflow,ventricularvolume,heartsounds,venouspulse,andtheelectrocardiogramforacompletecardiaccycleinahumansubject.Isovol,isovolumic.
systole.
In a normal heart, the valve leaflets remain relatively close together during ventricular filling. The partial approximation of the valve surfaces during diastole is caused by eddy currents that prevail behind the leaflets and by tension that is exerted by the chordae tendineae cordis and papillary muscles.
CHAPTER 16 Elements of Cardiac Function •Fig. 16.40 Illustrationofaheartsplitperpendiculartotheinterventricularseptumtodepicttheanatomicalrelationshipsoftheleafletsoftheatrioventricularandaorticvalves.Pulmonary artery Left atrium Left auricular appendage Mitral valve—anterior cusp Pulmonary veins Superior vena cava Aorta Aorta Mitral valve— posterior cusp Right ventricle Left ventricle Left ventricle Papillary muscle Papillary muscles appendage Orifices of coronary arteries Posterior cusp Anterior cusp •Fig. 16.41 Illustrationoffourcardiacvalvesasviewedfromthebaseoftheheart.Notehowtheleafletsoverlapintheclosedvalves.Anterior cusp Right cusp Left cusp Posterior cusp Anulus fibrosus Medial cusp valve
The pulmonic and aortic valves are located between the right ventricle and the pulmonary artery and between the left ventricle and the aorta, respectively. These valves consist of three cup-like cusps that are attached to the valve rings (see
Figs. 16.40 16.41 ). At the end of the reduced ejection phase of ventricular systole, blood flow briefly reverses toward the ventricles. This reversal of blood flow snaps the cusps together and prevents regurgitation of blood into the ventricles. During ventricular systole, the cusps do not lie back against the walls of the pulmonary artery and aorta; instead, they float in the bloodstream at a point approximately midway between the vessel walls and their closed position. Behind the semilunar valves are small outpocketings (sinuses of Valsalva) of the pulmonary artery and aorta. In these sinuses, eddy currents develop, which tend to keep the valve cusps away from the vessel walls. Furthermore, the orifices of the right and left coronary arteries are behind the right and the left cusps, respectively, of the aortic valve. Were it not for the presence of the sinuses of Valsalva and the eddy currents developed therein, the coronary ostia could be blocked by the valve cusps, and coronary blood flow would cease.
The Pericardium